ENABLE Reference Manual

ENABLE ATTRIBUTES
TREE Attribute
Choosing the Parent and Child Box. To determine which box is to
be the parent box and which box is to be the child box, consider
the purpose for which you are generating the application. Under
most circumstances, you should make the box associated with the
records in which you are most interested the parent box.
Remember, the application cannot read or insert a record for the
child box unless a matching record exists for the parent box.
When you decide which box is to be the parent box and which is to
be the child, you also affect the appearance of the terminal
screen displayed by an application. Remember, an application
always displays the join field of the parent box on the screen
line that directly precedes the child box.
ENABLE has two other requirements that should affect your
decision. These requirements are:
1. The size of the join field of a parent box must be smaller
than or equal to the size of the join field for a child box.
To determine the size of a join field, examine the PIC clause
of the field in the record description. Besides identifying
the data type of the field, this clause also defines the
number of characters that the field can store. Consider, for
example, the following PIC clauses and the corresponding
number of characters that they define for a field:
Number of Characters in the
PIC Clause Field___________
PIC 9(4). 4 characters
PIC X(20). 20 characters
PIC 9(4)V99. 6 characters
PIC A(30). 30 characters
For COMP fields the number of 9s represented by the PIC
clause determines the number of characters in the field as
follows:
Number of 9s Number of Characters
1-4 (For example, PIC 9(3)) 2
5-9 (For example, PIC 9(6)) 4
10-18 (For example, PIC 9(11)) 8
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